JPH08329804A - Proximity sensor of electrostatic capacitance type - Google Patents

Abstract

PURPOSE: To provide a proximity sensor of electrostatic capacitance type which can prevent erroneous sensing resulting from liquid attachment to a sheath case for an electrode by giving water repellency to the outer surface of the sheath case. CONSTITUTION: A sheath case for a proximity sensor of electrostatic capacitance type is formed from an upper plate 1 and lower plate 2, and the sensing direction of a sensing electrode 3 (for example, as per Arrow B) is set by a shield plate 4, and the electrode 3 and shield plate 4 are joined with a circuit board 5 in electrical connections. The surface on Side A (sensing surface) of the upper plate 1 is provided at least partially with a coating film 1a consisting of a water repellent material. Thereby no water exists on the sensing surface even though the sheath case is put in a bedewing environment, and it is possible to sense approach of an object due to change in the electrostatic capacitance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type proximity sensor.

[0002]

2. Description of the Related Art As a conventional capacitance type sensor, a pulse generating circuit, two delay circuits for branching the output of the pulse generating circuit into two, and delaying each output, and these two delay circuits. Having a detection electrode connected to at least one of them, the capacitance of which changes depending on the proximity of an object, and a phase discriminating circuit which judges the lead / lag of the phases of the output signals of the two delay circuits and outputs the detection signal. There is.

[0003]

However, in the above-mentioned case, when the surface of the outer case of the detection electrode is condensed due to a sudden change in environment, or when water drops are attached to the surface of the outer case due to rain or the like. However, there is a problem that the capacitance of the detection electrode changes due to these water contents, and the sensor erroneously detects due to the change in the capacitance.

An object of the present invention is to provide a capacitance type proximity sensor capable of preventing erroneous detection due to liquid adhering to the outer case of the detection electrode.

[0005]

According to the present invention, in a capacitance type proximity sensor for detecting the proximity of an object by a change in capacitance, at least a part of the outer surface of the outer case of the detection electrode of the capacitance is emitted. The above-mentioned object is achieved by having an aqueous property.

The outer surface of the outer case is preferably a curved surface or an inclined surface.

It is desirable to provide a drainage channel at the lower end of the inclined surface or curved surface.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments shown in the drawings.

In FIG. 1A, reference numeral 1 denotes an upper plate, which is made of a plastic material or the like. The surface A of the upper plate 1 (hereinafter referred to as the detection surface) is coated with a water-repellent material.
a is formed. Examples of the water-repellent material include a fluororesin-based coating material and a silicone resin-based coating material. Specifically, Sumitomo 3M's "Florard" is used as the fluororesin coating material, and Toray Co., Ltd. is used as the silicone resin coating material.
Dow Corning Silicone "CY52-005"
Etc. can be used. A lower plate 2 is made of a plastic material or the like. The upper plate 1 and the lower plate 2 constitute an outer case of a sensor unit described later. Reference numeral 3 denotes a detection electrode, the detection direction of which is set by the shield plate 4. In this example, the arrow B direction is set as the detection direction. Reference numeral 5 is a circuit board on which the circuit of the capacitance type sensor is mounted. The detection electrode 3 and the shield plate 4 are electrically joined to the circuit board. Note that FIG. 1B is a reduced front view from the direction of arrow C in FIG.

Next, the circuit configuration of the capacitance type sensor is shown in FIG.
Will be described with reference to. The components having the same numbers as those in FIG. 1 are the same.

In the figure, 6 is a pulse generator, which outputs a rectangular wave. Reference numeral 7 is a delay circuit, which is composed of a constant current circuit 8, a switching circuit 9, a resistor 10, a capacitance component 11, etc., and is connected to the detection electrode 3. A delay circuit 12 includes a constant current circuit 13, a switching circuit 14, a resistor 15, and a capacitance component 1.
It consists of 6 mag. Reference numerals 17 and 18 denote binarization circuits, which are configured by Schmitt circuits or the like, for example. Constant current circuit 8, 13
Outputs a substantially constant current while the pulse generator 6 is generating a pulse, and the switching circuits 9 and 14 are closed when the pulse generator 6 does not generate a pulse. Therefore, while the pulse generator 6 is generating a pulse, the capacitance components of the delay circuits 7 and 12 are charged with a substantially constant current, and when the pulse is not generated, the capacitance components of the delay circuits 7 and 12 are charged. The electric charges are discharged through the resistors 10 and 15, respectively. 19
Is a phase discrimination circuit, which compares the phases of the output signals of the binarization circuits 17 and 18 and outputs a signal indicating the lead or lag thereof, that is, a detection signal. 20 is an inverter.

Next, the operation will be described with reference to FIG. In the figure, Pa to Pf are terminals Pa to Pf in FIG.
Shows the output level of.

In the normal state where the object is not approaching (the period of TN in FIG. 3), the delay amount of the delay circuit 7 is set to the delay circuit 12.
The output of the binarization circuit 18 is slightly behind the output of the binarization circuit 17 (see FIG. 3P).
c, Pe)). At this time, the terminal P of the phase discrimination circuit 19
The detection signal to f becomes "0", and it can be confirmed that there is no object nearby.

When an object approaches the detection electrode 3 (TK in FIG. 3)
Period), the capacitance of the capacitance component of the delay circuit 7 increases, so that the delay amount of the delay circuit 7 increases and becomes larger than the delay amount of the delay circuit 12, and the output binarized by the binarizing circuit 17 Is delayed from the output binarized by the binarization circuit 18. Therefore, the detection output of the phase discrimination circuit 19 is inverted to "1", and the proximity of the object can be confirmed.

In this example, since the water-repellent coating 1a is provided on the outer surface of the outer case arranged in the detection direction of the detection electrode 3, that is, the detection surface, the outer case is placed in a dew condensation environment, for example. Is no longer present on the outer surface (detection surface) of the outer case arranged in the detection direction of the detection electrode 3,
Moreover, since the amount of the delay circuit 7 is small even if it exists, the capacitance of the delay circuit 7 which is increased by the moisture is small, and the phase discrimination circuit 19
The output state to the terminal Pf can be maintained at "0", and erroneous detection can be prevented.

More specifically, when the outer case is exposed to a dew condensation environment, the water vapor in the air increases its volume by trying to become water as a liquid with fine dust on the surface of the outer case as a nucleus. To go. However, since the water-repellent material has a large contact angle at the interface with water, the increase in the volume of water is suppressed as compared with the case where there is no coating made of the water-repellent material, and the amount of water does not increase to the extent that malfunction occurs. Even if the amount of water increases, the contact angle at the interface between the water and the water-repellent material is large, so that water does not wet the surface A (detection surface) of the upper plate 1, and as in the example described later, When the surface A is slightly inclined with respect to the vertical surface in the vertical direction, water cannot stay on the surface A and moves to a place other than the surface A. Therefore, even if the outer case is in a dew condensation environment, A of the upper plate 1 which is the detection surface
Almost no water is present on the surface (detection surface), and malfunction due to dew condensation can be prevented.

The present invention can be applied not only to the phase discrimination type capacitance type sensor, but also to other types of capacitance type sensors to obtain the same effect.

In the above example, the outer case is provided with a water-repellent coating, but the outer case may be formed of a water-repellent material (for example, "Aflon COP" manufactured by Asahi Glass Co., Ltd.).

The detection surface of the outer case 1 may be an inclined surface 21 or a curved surface 22 as shown in FIGS. 4 to 9 in order to facilitate the movement of water attached to the outer case having the detection surface. In each figure, the same numbers as in FIG. 1 are the same.

In FIG. 4, the detection surface of the upper plate 1 is an inclined surface 21. FIG. 4B is a sectional view taken along the line dd of FIG. Referring to FIG. 4 in detail, a groove is provided from the top 1a to the ends 1b and 1c, and the ends 1b and 1c are provided with grooves 1d and 1 which are inclined downward in FIG. 4 (a).
e is provided. The grooves 1d and 1e form a drainage channel. Therefore, the liquid adhering to the detection surface rolls down the slope and falls into the grooves 1d and 1e, and moves to the outside of the detection surface due to the inclination provided in the grooves 1d and 1e, so that the liquid further adheres to the detection surface. In addition to the difficulty, the liquid can be removed from the outer case faster. In addition, the groove 1d,
1e is provided at a position that does not affect the detection performance of the sensor regardless of the presence or absence of water droplets. The shape of the detection surface is not limited to the above, and may be, for example, an arc shape as shown in FIG.

Further, as shown in FIGS. 5, 6 and 7, the detection surface is formed as an inclined surface 21 or a curved surface 22 so that the inclination of the detection surface is not limited to one direction (the direction of the arrow D in the drawing) but also to other directions. A slope may be provided.

Further, a drainage channel as shown in FIG. 4 may be provided at the lower end of the inclined surface or curved surface of FIGS.

Further, the detection surface may be an inclined surface as shown in FIGS. 8, 9 and 10. The inclined surface in FIG. 10 may have a shape as shown in FIG.

Incidentally, in FIGS.
10 (a) is a front view in the direction of arrow E in FIGS. 5 (b) to 10 (b), and FIGS. 5 (c) to 10 (c) are
It is a front view in the arrow F direction of Drawing 5 (b) -Drawing 10 (b), respectively.

[0025]

According to the present invention, at least a part of the outer surface of the outer case of the capacitance detection electrode is made water-repellent in the capacitance type proximity sensor for detecting the proximity of an object by the change of the capacitance. It is possible to prevent erroneous detection due to the liquid adhering to the outer case. For example, even when the outer case is placed in the dew condensation environment, it is possible to prevent erroneous detection due to dew condensation.

If the outer surface of the outer case is formed into a curved surface or an inclined surface, this inclination makes it more difficult for liquid to adhere to the outer case, and therefore erroneous detection due to dew condensation can be prevented.

If the drainage channel is provided at the lower end of the inclined surface or the curved surface, the liquid can be removed from the outer case faster in addition to the above effect.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a main part of FIG.

FIG. 3 is a timing chart for explaining the operation of FIG.

FIG. 4 is an explanatory view showing another embodiment of the present invention.

FIG. 5 is an explanatory diagram showing another embodiment of the present invention.

FIG. 6 is an explanatory view showing another embodiment of the present invention.

FIG. 7 is an explanatory view showing another embodiment of the present invention.

FIG. 8 is an explanatory view showing another embodiment of the present invention.

FIG. 9 is an explanatory view showing another embodiment of the present invention.

FIG. 10 is an explanatory view showing another embodiment of the present invention.

[Explanation of symbols]

 1 Outer case 3 Detection electrode 21 Inclined surface 22 Curved surface

Claims (3)

[Claims] 1. A capacitance type proximity sensor for detecting the proximity of an object based on a change in capacitance, wherein at least a part of an outer surface of an outer case of the capacitance detection electrode is water-repellent. Characteristic capacitive proximity sensor. 2. The capacitance type proximity sensor according to claim 1, wherein the outer surface of the outer case is a curved surface or an inclined surface. 3. The capacitance type proximity sensor according to claim 2, wherein a drainage channel is provided at a lower end portion of the inclined surface or the curved surface.